1. Field of the Invention
The present invention relates to a method and an apparatus for the purpose of regulating the combustion characteristics of a gaseous fuel, and more particularly to the calorific power conveyed by a stream of gaseous fuel, especially a stream of fossil fuel of the natural-gas type.
The present invention relates especially to regulation of a stream of gaseous fuel distributed by a network of feed pipes to industrial plants using a thermal process, the regulation according to the invention preferably taking place at the downstream end of the said network, on the site of the industrial plant, or just upstream of the latter.
2. Description of the Background
The industrial plants more particularly intended are glassmaking plants using natural-gas burners for melting (and possibly refining) glass in the widest sense, that is to say mineral compositions used to manufacture flatware (float lines), hollowware (plants for making bottles and flasks), mineral wool of a glass type or rook type intended for thermal and/or acoustic insulation, or glass fibers used for the reinforcement of polymeric-type materials, called reinforcing figures, or else textile fibers.
In all these types of plant, it is important for the furnaces to operate under the most constant and uniform conditions as possible, one parameter among others, which is not insignificant, being the properties of the fuel which feeds the burners, especially its calorific power. Now, it may happen that the distribution network delivers a natural gas whose properties fluctuate for various reasons, the most frequent of which is the fact that the network is fed with natural gas having different properties coming from several sources of supply.
It has therefore proved necessary to take corrective actions in order to compensate for these variations in calorific power.
A first mode of regulation has consisted in varying the flow of the fuel, by making a high-value correction to its calorific power by increasing its flow rate, or by making a low-value correction by decreasing its flow rate with a non-combustible gas in order to reduce its flow rate, the flow corrections taking place in the same proportions as the observed fluctuations in the calorific power of the fuel. This mode of regulation makes it possible to maintain the calorific flow entering the furnace at its set value. Whether this regulation is carried out manually or automatically, their limits have quickly been reached; this is because it has been observed that simply correcting the calorific power of the incoming gas by proportional modulation of the flow rate does not achieve perfect stabilization of the furnace operating conditions, all other things being equal. This could be explained by the fact that variations in the fuel flow rates at the burners also cause modifications in the manner in which the combustion takes place and, especially, the manner in which the flame will develop above the glass bath.
Accordingly, there remains a need for new methods of regulating the calorific power of fuel gases.
An object of the invention is to provide an improved mode of regulation for the calorific power of a stream of gaseous fuel, especially with the aim of minimizing any modification induced by the regulation itself in the manner in which the combustion takes place. In particular, an object of the invention is to achieve a regulation which preserves as far as possible the stability of the operating conditions of the furnace, when the fuel is intended to feed the burners of a furnace of the glass-furnace type.
Accordingly, the present invention provides a method of regulating the calorific power of a stream of gaseous fuel of the fossil-gas type comprising predominantly a gas, denoted xe2x80x9cAxe2x80x9d, and flowing in a pipe. It consists in carrying out the regulation, at least partly, by the controlled addition of at least one combustible gas, denoted xe2x80x9cBxe2x80x9d, having a calorific power greater than that of A into the stream.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description.